Equipment for Measurement and Control of Load Material or Scrap Feeding Into a Furnace and Relative Method

ABSTRACT

An equipment for the measurement and control of load material and scrap metal feeding into an electrical arc furnace, including an automatic control device for feeding control of load material or scrap according to the energy supplied to the bath, and a measuring device for the added load material, in correlation with the automatic control device, comprising a weighing device for the furnace shell, its contents and any other components it may support.

The present invention relates to equipment for the measurement andcontrol of feeding load material and scrap into a furnace and therelative method, in particular for the measuring and control ofcontinuous feeding.

The use of continuous systems for loading scrap metal into a furnace, inparticular in an electric arc furnace (EAF) for steel production,systems such as CONSTEEL® for example, and/or the addition of previouslyreduced material to the bath, involves the need for maintaining directcontrol of the load material flow as it enters the furnace.

In fact, if the continuous addition of load material in solid state isnot continuously and correctly controlled, this can cause problems thatreduce the overall efficiency of the productive cycle.

Among these problems, the most important is the formation of thickenedsolid material in the scrap unloading zone in the furnace, as itmaintains this consistence for a long period of time, thus prolongingthe smelting time in the furnace, and as a result, prolonging the wholeproductive cycle.

This control is equally as important in order to guarantee that theelectrical power supply to the electrodes is as homogeneous as possible,also avoiding direct contact between solid material and the electrodes,a contact that could cause the rupture of the electrodes.

In normal practice, said control is performed by an operator, the linecontroller, who manually regulates the scrap loading system speedaccording to his personal experience and his impression of the amount ofload material or scrap loaded in the furnace. Naturally this operatormust be extremely familiar with the process and the installation, and inany case his decisions can still always be affected by uncertain and notvery reliable data reading.

One solution for resolving these problems was to provide for theinclusion of continuous furnace shell weight control means.

To achieve this aim, two types of measurement were developed: anindirect furnace shell weight control method based on the level of theliquid metal, and a more direct control method based on sensors thatmeasure the system weight.

The indirect control method is based on geometric methods which,beginning with a reading of the liquid level, convert this data tovolume data (and therefore weight), a conversion that clearly depends onthe presumed profile of the refractory tank inside the furnace shell.

However, the furnace shell profile is strictly linked with erosivephenomena that the liquid metal provokes in the refractory, phenomena,which are often violent and unpredictable. Inevitably with time, thisresults in a lack of precision in the taring curve used to compare thelevel reading and the volume calculation. Considering said lack ofprecision and the high specific weight of iron, the measured data willreveal quite a large error, and therefore this technique cannot be usedfor precision control.

In the case of the direct control method, a method that is based on adirect weighing of the furnace shell structure, the weight readingsystems must be located in specific zones such as support uprights andbeams, which however, support not only the weight of the furnace shell,but also all the support structures, systems and sub systems of thefurnace. Therefore the amount of the load material or scrap metalincluded constitutes only a limited percentage fraction of the measuredweight, and this involves all the various aspects of lack of precision.This lack of precision becomes so great that any measurements performedcan be considered reliable only as far as quality is concerned.

In the case of wheel mounted tilting furnaces (and with the weighingsystem on the wheels), it is the weight of the furnace shell tiltingsystem that must be able to resist strong mechanical stress, to raisethe total read weight sacrificing measurement precision.

The general aim of the present invention is therefore to resolve theaforesaid problems in a simple, economical and particularly functionalmanner.

It is an object of the present invention an equipment for measuring andcontrolling load material or scrap metal feeding into an electric arcfurnace, having an automatic device to control load material or scrapmetal feeding according to the energy supplied to the bath, plus adevice for measuring the amount of added load material, in correlationwith the automatic control device, comprising a device to weigh thefurnace shell, its contents and any other components it may support.

It is another object of the present invention is a method for measuringand controlling the feeding of the load material or scrap metal into anelectric arc furnace that includes the following steps:

-   -   weighing of the load material or scrap metal added to the bath,        performed by a device that weighs the furnace shell, its        contents and any other components it may support;    -   data acquisition of a measurement reading of the amount of load        material or scrap metal added to the bath, supplied by the        weighing device, said reading being differential over a period        of time for example;    -   optimising the load flow according to suitable algorithms,        obtained by adjusting the feeding speed of the load material or        scrap metal according to the energy supplied to the bath;

Preferably, the feeding of the load material or scrap metal into anelectric arc furnace should be continuous.

In particular, the weighing device of the furnace shell and any othercomponents it may support, provides for a support structure for thefurnace shell composed of support rollers.

The function of such rollers is to recover any deviation in shapeinduced by the heat cycle.

Furthermore the weighing device operates with dual redundancy, at leaston two of the support rollers that comprise the measuring rollers.Therefore, preferably at least two support rollers mounted on theequipment according to the present invention act as measuring rollers.

The measuring rollers are equipped with sensors for direct or indirectweight reading.

A third support roller can also act as a measuring roller equipped withsensors for direct or indirect weight reading.

In particular, also, the automatic device for controlling the feeding ofthe load material or scrap metal includes connection and control systemsfor the means used to feed or load the load material or scrap.

Basically, the automatic device or system for management and control,acquires a reading of the precise measurement supplied by the weighingdevice, differential over a period of time, which measures in acontinuous manner the amount of load material or scrap metal added tothe bath, by weighing the furnace shell, its contents and all componentsit may support.

According to the algorithms for optimising the load flow, the automaticmanagement and control system thus operates on the scrap metal feedingspeed to prevent any solid agglomerates that form from being sent intothe bath at any energy level whatsoever (electrical and/or chemical).

A main advantage of the equipment and method according to the presentinvention, is the fact that by controlling the ratio between thesupplied energy and weight of loaded material (scrap), the temperatureof the liquid metal can be controlled, maintaining it close to the idealvalue for the cycle, and being able to operate constantly at the maximumenergy yielded to the bath, and therefore contributing towards raisingthe productive efficiency.

Furthermore, this helps prevent any human errors caused by lack ofprecision in operating condition calculations. Yet a further advantageis the reduction in requests for technical information from the headoperator on the line who will have the support of a system able toanalyse conditions in real time and thus help him to make theappropriate decisions automatically and in real time.

As far as the weighing device is concerned, the solution adoptedaccording to the present invention is particularly advantageous, as itis based on a choice of general furnace configuration derived from awell-tested design and constructive scheme, but with the addition of adata acquisition method that is absolutely innovative.

The constructive scheme of the furnace proposed is based on theseparation of the various functions: the function of containing thesmelted material requires a compact structure, as light as possible,comprised of only the furnace shell and any other components it maysupport.

The support and tilting of the furnace shell (during tapping, thecomplete emptying of the furnace shell for maintenance or remaking)require a support structure from underneath. This configuration has beendemonstrated as the most suitable for the application of the weighingsystem since it is that which provides the best ratio between treatedmaterial, in other words, the load material or scrap metal to be fedinto the furnace, and the total weight applied on the weighing system.

In fact, in the solution according to the present invention, the furnaceshell weighs on the support structure by means of the rollers, whoseadditional function is to recover any deviation in shape induced by theheat cycle. Such rollers support the structure involved in smelting aslittle as possible, and therefore they are the best solution forproviding efficient instrumentation aimed at monitoring the weight ofthe scrap metal to be added.

Given the geometry of the coupling between the furnace shell and thesupport structure however, other embodiments are possible, such asprecision measuring systems to calculate the distance between thefurnace shell body and the support structure or any furnace shellweighing system suitable for controlling scrap metal or load materialfeeding.

The equipment and method according to the present invention are alsoapplicable to all operating methods that involve the addition of liquidor solid metal, in a more or less continuous manner during the operatingcycle.

Although the particular equipment and method for the measuring andcontrol of load material and scrap metal feeding into furnaces for steelproduction, is closely linked with the specific constructive scheme ofthe furnace shell, it can also be applied to other methods.

It is another object of the present invention to provide a method forsteel refining comprising:

-   -   continuous preheating of the load material;    -   feeding of said material containing iron, directly reduced iron,        or a blend of both into an electric arc furnace in order to        perform smelting and refining operations;    -   feeding of elements to form slag in the bath for steel        production;    -   introduction of carburizing elements into the furnace for steel        production;    -   electrical heating of the load using electrodes to melt the load        and form a bath of melted metal in the furnace with a layer of        melted slag on said melted metal bath;    -   maintaining said slag in a foamy condition during the steel        production process;    -   feeding of metal elements, as slag formers, and carburizing        elements into said furnace;    -   maintaining full electrical power capacity in said furnace for        the total loading, smelting and refining time;    -   intermittent tapping from the furnace maintaining a liquid metal        heel inside the furnace shell, said liquid metal heel        approximately representing a weight that varies between 10% and        30% of the weight prior to tapping;        such method being characterised in that the load material or        scrap metal feeding step, that is materials containing iron,        directly reduced iron, or a blend of both, in an electric arc        furnace, comprises the following sub-steps:    -   weighing of the load material or scrap metal added to the bath,        supplied by a weighing device through the weighing of the        furnace shell, its contents and any components it may support.    -   data acquisition of a measurement reading of the amount of load        material or scrap metal added to the bath, and supplied by the        weighing device, differential in time for example.    -   optimising of the load flow according to suitable algorithms        through regulating the load material or scrap metal feeding        speed, according to the energy supplied to the bath.

It is another object of the present invention to provide equipment forrefining steel comprising:

-   -   an electric arc furnace for steel production, for smelting and        refining a load of metal inside the furnace;    -   electrodes that extend inside the furnace as far as the        intermediate slag level and the level of the smelted material        contained in the bath;    -   a feeding means connected to said furnace for the introduction        of load materials inside said furnace without the removal of the        electrodes;    -   post-combustion means associated to cooperate with said feeding        means in order to preheat the load materials inside said feeding        means;    -   means for measuring and controlling load material or scrap metal        feeding composed of an automatic control means for the load        material or scrap metal, and a means for measuring the added        load material, in correlation with the automatic control device;    -   a hermetically sealed mechanical device located in the inlet        section of the load material or scrap metal to the feeding        means;    -   gas injection means that communicate with said furnace above        and/or below the normal melted metal level in the bath; and    -   means for tilting said furnace for slagging and tapping        operations, the tapping means being positioned in a manner so        that said slant of said furnace will maintain a heel of melted        liquid material inside said bath, said heel having a weight that        varies approximately between 10% and 30% of the weight prior to        tapping.

The structural and functional characteristics of the present inventionand its advantages in relation to prior technical art will be madeclearer and more obvious from the following description, with referenceto the appended drawings wherein:

FIGS. 1 and 2 are side elevation views of technical solutions accordingto the state of the art;

FIGS. 3 and 4 are side elevation views of an embodiment of the systemaccording to the present invention;

FIG. 5 is a block diagram of the method according to the presentinvention.

In particular, FIG. 1 shows an EAF furnace whose tilting platform (5)(for slagging, tapping or emptying operations) is supported by wheels(3) positioned on support bases (6).

The furnace shell (1) is set by means of suitable supports (2) on thetilting platform (5).

The side opening (4′) is used to feed the scrap metal, by means of aconveyor (4) if necessary, with a continuous feeding procedure such asthat provided by the CONSTEEL® system, for example. The traditionalconfiguration is sometimes equipped with instruments for reading theweight by means of sensors located in the axes of the EAF furnacesupport wheels (3).

On the other hand, the embodiment shown in the FIGS. 3 and 4, refers tothe invention according to the present invention. The tilting platform(5) is mounted on the support base (6), and the furnace shell (1) is seton suitable supports (2) on the platform. In order to allow forstructural settling due to the temperature, the furnace shell supportsystem is composed of at least two rollers (7). The weight readers orsensors are mounted inside such rollers (7). Purely as an example, andby no means in a limiting manner, these sensors can be mounted with dualredundancy in the roller (7) axes and be composed of shearing stresssensors. The weighed portion is composed of the furnace shell (1) only,as shown in FIG. 3, which weighs much less than that shown in FIG. 1(furnace shell (1) plus tilting platform (5)), and therefore the sensorsin the rollers (7), under less strain, can be designed with far greaterprecision capacity.

The data acquisition reading (see FIG. 5) together with a suitablecalculation algorithm, permits step monitoring of the scrap metalfeeding into the furnace shell (1) in real time through the opening (4′)by means of the conveyor (4). The data acquisition system (FIG. 5) thenprocesses said information, also according to the energy at the furnaceinlet, making it available for the line operator, as well as for thecontinuous scrap metal feeding control system (4) as described in FIG. 5(such as the Consteel® system, for example).

Alternatively, in the case of tilting furnaces without wheels (as in thetype shown in FIG. 2 in the version according to present state of theart) whose weight is not nearly as easily measured, the application ofthe solution according to the present invention allows real timemeasurement (FIG. 4) of the load material and has a considerableinfluence on the simplification of the construction of EAF furnacesystems with possible continuous feeding equipment (the Consteel®system, for example).

The term load material or “scrap metal” used in the present descriptionand in the subordinate claims refers to the load material for continuoussmelting, comprised of iron scrap, cast iron, directly reduced iron inthe form of peens or fragments and/or a blend of both.

In particular, through data acquisition measurement reading of theamount of load material or scrap metal added to the bath by means of theweighing device, differential in time for example, load flow optimisingcan be calculated according to suitable algorithms. According to thisdata, the equipment and method management and control device regulatesthe load material or scrap metal feeding speed.

1. Equipment for the measurement and control of load material and scrap metal feeding into an electrical arc furnace, which provides an automatic control device for feeding load material or scrap according to the energy supplied to the bath, and a measuring device for the added load material, in correlation with the automatic control device, comprising a weighing device for the furnace shell, its contents and any other components it may support.
 2. Equipment according to claim 1, characterised in that the weighing device for the furnace shell, its contents and any other components it may support, provides a furnace shell support structure by means of support rollers.
 3. Equipment according to claim 2, characterised in that at least two support rollers are composed of measuring rollers.
 4. Equipment according to claim 3, characterised in that the measuring rollers are equipped with sensors for direct or indirect weight reading.
 5. Equipment according to claim 3, characterised in that a third support roller is also a measuring roller equipped with sensors for direct or indirect weight reading.
 6. Equipment according to claim 1, characterised in that the automatic control device for load material or scrap metal feeding provides connection and control systems on the feeding or loading means for the load material or scrap metal.
 7. Equipment according to any one of the previous claims, characterised in that the feeding of the load material into the furnace is continuous.
 8. Use of the equipment according to claim 1 in operating procedures that provide the adding of liquid or solid metal in a more or less continuous manner during the operating cycle.
 9. Method for measuring and control of load material or scrap metal feeding into an electric arc furnace, that provides the following steps:—weighing of added load material or scrap metal into the bath, supplied by a weighing device, through the weighing of the furnace shell, its content and any other components it may support; data acquisition of a measurement reading of the amount of load material or scrap metal added to the bath, supplied by the weighing device, differential in time for example; optimising of the feed flow according to suitable algorithms, through load material or scrap metal feeding speed regulation according to the energy supplied to the bath.
 10. Method according to claim 9, characterised in that the weighing of the load material is performed by any weight measuring method whatsoever.
 11. Method for steel refining comprising:—continuous preheating of the load material; feeding of said material containing iron, directly reduced iron or a blend thereof, into an electric arc furnace for smelting and refining; feeding of slag forming elements into the bath for steel production; introduction of carburizing elements into the furnace for steel production; electrical load heating by means of electrodes to melt the load and form a bath of melted metal inside the furnace, having a layer of melted slag on said bath of melted metal; maintaining said slag in a foamy condition during the steel production method; feeding of metallic elements slag formers, and carburizing elements into said furnace; maintaining full electric power capacity in the furnace for the total loading, smelting and refining time; intermittent furnace tapping, maintaining a liquid heel of melted metal inside the furnace shell, said liquid heel being equal to a weight between approximately 10% and 30% of the weight prior to tapping; said method being characterised in that the feeding stage of load material or scrap metal (of materials containing iron), directly reduced iron, or a blend of both in an electric arc furnace, comprises the following sub-steps: weighing of the load material or scrap metal added to the bath, supplied by a weighing device through the weighing of the furnace shell, its contents and possible other components it may support; data acquisition of a measurement reading of the amount of load material or scrap metal added to the bath, supplied by the weighing device, differential in time; optimising of the load flow according to suitable algorithms through load material or scrap metal feeding speed regulation, according to the energy supplied to the bath.
 12. A method according to claim 9, characterised in that the feeding of the load material into the furnace is continuous.
 13. Equipment for steel refining comprising: an arc furnace for steel production for smelting and refining a metal load inside said furnace; electrodes that extend inside said furnace as far as the intermediate level between the slag level and the level of the melted material contained in the bath/feeding means connected to said furnace for the introduction of load materials inside said furnace without the removal of the electrodes; post-combustion means associated to cooperate with said feeding means for preheating the load materials inside said feeding means; means for measuring and controlling the load material or scrap metal feeding, comprising an automatic load material or scrap metal feeding control device, and a measuring device for the added load material, in correlation with the automatic control device; a hermetically sealed mechanical device located in the load material inlet section to the feeding means; gas injection means that communicate with said furnace above and/or below the normal level of the melted metal in the bath; and means for tilting said furnace for slagging and tapping operations, said tapping means being positioned in a such a manner that said slant of said furnace is able to maintain a heel of melted liquid material inside said bath, said heel having a weight that is approximately between 10% and 30% of the weight prior to the tapping stage.
 14. Equipment according to claim 13, characterised in that the feeding of the load material into the furnace is continuous. 